Why is transurethral microwave thermotherapy (TUMT) positively effective?

Between 1992 and 1994, 157 patients with benign prostatic hyperplasia were treated with transurethral microwave thermotherapy (TUMT). In evaluating the efficacy of TUMT with the International PrOstate Symptom Score (I-PSS) in 121 patients, 18 (15%) showed excellent and 42 (35%) showed good response. In evaluation of QOL, the result was 43 patients (33%) excellent and 42 patients (35%) good response. In objective evaluation of uroflow in 93 patients, 12 (13%) showed excellent and 13 (14%) showed good response. The prostatic volume did not show a significant decrease after treatment. In terms of overall improvement, according to the criteria proposed at the 2nd International Consultation on BPH, the treatment was considered effective in 53 of 108 patients (48%). Histological examination of the prostate enucleated from a patient 7 months after TUMT revealed degenerative changes of nerve fibres on S-100 protein immunohistochemical staining, which were more extensive than those in smooth muscle cells on HE staining. In in vitro tests the isometric contraction force of the rabbit prostatic tissue was measured after exposure to different temperatures, ranging from 37 to 50 degrees C. No significant change was observed up to 45 degrees C vs. 37 degrees C. After exposure to 48 degrees C, the nerve mediated contractions became completely depressed, although phenylephrine or KCl induced contractions were only partially suppressed. After exposure to 50 degrees C, no contraction was induced by any type of stimuli. In conclusion, it is suggested that good symptomatic improvement after TUMT results from both neural and muscular damage to the prostate. As TUMT is not aiming at a relief of anatomical obstruction, 50 degrees C is thought to be a sufficient thermal condition to cause an irreversible damage to prostatic tissue, which will provide a relief from functional obstruction and urethral instability.